Context 3.x API
---------------
The following is an overview of using the Context API.


The context static cache
------------------------
Context provides a centralized set of API functions for setting and retrieving a
static cache:

    // Set a static cache value at [my_namspace][mykey]
    context_set('my_namespace', 'mykey', $value);

    // Retrieve a static cache value at [my_namespace][mykey]
    context_get('my_namespace', 'mykey'); // $value

    // Boolean for whether there is a value at [my_namespace][mykey]
    context_isset('my_namespace', 'mykey'); // TRUE

These are used internally by context but may also be used by other modules. Just
do not use the namespace `context` unless you want to affect things that context
is up to.


Adding a condition or reaction plugin
-------------------------------------
Both context conditions and reactions utilize the CTools plugins API. In order
to add a new condition or reaction for your module, follow these steps:

1. Implement `hook_context_plugins()` to define your plugins, classes, and class
  hierarchy.

        function mymodule_context_plugins() {
          $plugins = array();
          $plugins['mymodule_context_condition_bar'] = array(
            'handler' => array(
              'path' => drupal_get_path('module', 'mymodule') .'/plugins',
              'file' => 'mymodule_context_condition_bar.inc',
              'class' => 'mymodule_context_condition_bar',
              'parent' => 'context_condition',
            ),
          );
          return $plugins;
        }

2. Implement `hook_context_registry()` to define your conditions and/or
  reactions and map them to plugins.

        function mymodule_context_registry() {
          return array(
            'conditions' => array(
              'bar' => array(
                'title' => t('Name of condition "bar"'),
                'plugin' => 'mymodule_context_condition_bar',
              ),
            ),
          );
        }

3. Write your condition or reaction plugin class. It's best to look at one of
  the included plugins as a starting point.

4. Add in a Drupal integration point for your plugin. A node page condition
  plugin, for example, may be invoked from `hook_nodeapi()`.


Replacing or extending existing plugins
---------------------------------------
You can replace a condition or reaction plugin with your own plugin class using
`hook_context_registry_alter()`:

    function mymodule_context_registry_alter(&$registry) {
      if (!empty($registry['conditions']['node'])) {
        $registry['conditions']['node']['plugin'] = 'mymodule_context_condition_customnode';
      }
    }

This entry would swap out the default node condition plugin for a custom one
provided by `mymodule`. Note that any replacement plugins must have an entry in
`hook_context_plugins()`.